New C plus plus notes

进制

十进制：20
八进制：024（以0开头）
十六进制：0x14（以0x或0X开头）

列表初始化

int a = 0;
int b(0);
int c = { 0 };//列表初始化
int d{ 0 };   //列表初始化

特点：使用列表初始化且初始值存在丢失信息的风险，编译器会报错

double a = 10.2;
//int x{ a };     invalid
//int x = { a };  invalid
//int x = { 1.3 };invalid
int x(a);         //valid, but d=10
int y = a;        //valid, but e=10

extern

单独使用：用于未提供定义的声明

#include <iostream>

extern int a;//未提供定义的声明
int main()
{
	int a = 1;
	std::cout << a;
}

extern const：在多个文件之间共享const对象

//.h
#pragma once

extern const int a;//valid
//const int b; invalid
const int b = 2;

void print();

//1.cpp
#include <iostream>
#include "MyProject.h"

extern const int a = 9;
int main()
{
	print();
}

//2.cpp
#include <iostream>
#include "MyProject.h"

void print()
{
	std::cout << a;
	std::cout << b;
}

enum

#include <iostream>

enum PlayerStatus
{
	PS_Crouched,
	PS_Standing,
	PS_Walking,
	PS_Running
};

int main()
{
	PlayerStatus Status;
	Status = PS_Crouched;
	if(Status==PS_Crouched)
	{
		std::cout << "PS_Crouched" << std::endl;
	}
	return 0;
}